Which of the following is NOT an eyelid gland?
The main eyelid glands are the Meibomian glands, which are sebaceous glands located in the tarsal plates. They secrete an oily substance that prevents tear evaporation. Then there are the glands of Zeis, which are sebaceous glands associated with the eyelash follicles. The glands of Moll are modified sweat glands also found at the eyelid margins. The lacrimal glands, however, are located in the upper outer part of the orbit and produce the aqueous layer of tears, not part of the eyelid itself. So if any option lists the lacrimal gland as an eyelid gland, that's incorrect. Other possible distractors might be the sebaceous glands of the eyelid, which are the Meibomian and Zeis. So the correct answer would be the lacrimal gland. I need to make sure each incorrect option is explained properly. Let me structure the explanation step by step.
**Core Concept**
This question tests knowledge of eyelid anatomy, specifically the classification of glands associated with the eyelids. The Meibomian, Zeis, and Moll glands are intrinsic to eyelid structure, while the lacrimal glands are extrinsic and located in the orbit.
**Why the Correct Answer is Right**
The **lacrimal glands** (Option D) are not eyelid glands. They are located in the superolateral orbit and secrete the aqueous component of tears. Eyelid glands include **Meibomian glands** (sebaceous, in tarsal plates), **glands of Zeis** (sebaceous, at eyelash follicles), and **glands of Moll** (apocrine, at eyelid margins). The lacrimal glands are anatomically and functionally distinct.
**Why Each Wrong Option is Incorrect**
**Option A:** Meibomian glands are **true eyelid glands** that produce lipid tears.
**Option B:** Glands of Zeis are **eyelid glands** associated with eyelash follicles.
**Option C:** Glands of Moll are **eyelid glands** (apocrine) at the eyelid margin.
**Clinical Pearl / High-Yield Fact**
Remember: **Meibomian glands** = "Meibom" sounds like "melt," hinting at their role in preventing tear evaporation. Lacrimal glands are often confused with eyelid glands but are **orbital** in location.
**Correct Answer: D. Lacrimal glands**